Just from personal experience (kk266-r) I've found the USB to actually work fine....
EXCEPT
With HP's crap drivers for the 930C in W98. Thought it must be the USB on my motherboard, after all it's VIA, but the mouse, gamepad, webcam, scanner all work fine, but try to print and it's reboot time. BTW, in W2K even the HP is happy.
It sounds like when you try to connect your DSL to USB (via a USB NIC I'm assuming) the USB dies. Same problem I had with my Soyo SYBA, a BX based board. It just couldn't handle any USB devices with much data flow. Like the webcam or the NIC I tried using. Seems in this way it varies board to board more than by chipset from what others said when I asked about my problems way back.
Not much help, just one of those "maybe if I share this, it'll spark an idea" posts.
--Mc